Runes

Greater Mark of Desolation Greater Mark of Desolation:
These are the must have runes for Renekton

Greater Seal of Vitality Seal of Vitality:
These are used to compensate the offencive tree i prefer

Greater Glyph of Shielding:
MR is always good to have

Quintessence of Fortitude:
Used to compensate the offencive masteries

Greater Quintessence of Regeneration Quintessence of Regeneration:
Used to compensate the offencive masteries

You can use flat runes if you like them more.

CDR is also a good thing to have so if you think you are needing it at the low levels consider Greater Glyph of Focus.

Masteries

Then About the masteries. I prefer Offencive tree, but if you like, the Defencive tree is also great to Renekton. I like to compensate Defensive tree with items like Force of Nature and Randuin's Omen.

Ofc, you need to modify masteries to fit your build, for ex. I take Haste because of Ghost

Summoner Spells

Ghost
Better spell for Renekton than Flash, we have already Slice and Dice and we need more chasing and fleeing speed.

Ignite
Nice counter to Champs like Mundo and great spell to cast on an running low HP enemy and just watch him/her die.

Items

Doran's Shield
This is the best starting item imho. You dont need any potions or anything but this and you can lane as long as you want.

Ionian Boots of LucidityCDR is must for Renekton so these would be a great choice.

Youmuu's Ghostblade
This is everything Renekton needs, Attack Damage, Armor Penetration and Cooldown Reduction. Also it's Active is unbelievable turret destroyer. With Active and Force of Nature you can solotank any turret down at level 10 or so.

Force of NatureMagic Resistance is the key to win. You'll be able to tank turrets, do tower dives and take no damage from magic damage dealers (the most annoying *****es against Renekton).

The Black Cleaver
This is the item Renekton lives for. Stackable Armor Reduction, Attack Speed and Attack Damage. With Ruthless Predator you can get maximum stacks instantly.

Randuin's Omen
This is also a great item for Renekton. We already have Magic Resistance and we could use a bit more Armor and Health. And it's Active is very powerful add in chasing and the most, in teamfights.

The Bloodthirster
We need ofc a little bit more Attack Damage, and with lifesteal, this is perfect item for it.

Item Sequence

We start with the [Doran's Shield] Doran's Shield. A little bit of Health regeneration and Armor is just perfect at the start. With just this we can lane forever.

Next two items we need are the Ionian Boots of Lucidity and The Brutalizer. You may prefer Ionian Boots over the The Brutalizer but I usually get just Boots of Speed and the The Brutalizer at the first B.

The next item depends on the team you are against to but I usually finnish the Ionian Boots of Lucidity and get some MR with Negatron Cloak so I am able to towerdive.

Next thing I do is finish the Youmuu's Ghostblade just because of its Active ability to take down towers. You may also prefer to get The Black Cleaver at this point.

Then its good to finish the Force of Nature or get The Black Cleaver. If opposing team has lots of Magic Damage dealers, go with Force of Nature first.

Last, but not least, we build Randuin's Omen and The Bloodthirster.

And if you have huge amounts of money, don't forget the Elixirs and Wards!

Considerable Items of Choice

Sunfire Cape
A very good item for Renekton because of it's passive. Choose this instead of Randuin's Omen

Quicksilver Sash
Very nice counter against the teams with CC. Consider taking with Mercury's Treads. Take this instead of Force of Nature

Mercury's Treads
An alternative choice of boots. Good choice against teams with lots of CC. Consider taking with or Banshee's Veil

Sword of the Occult
Snowballing the Attack Damage. Take this instead of The Bloodthirster

Infinity Edge
Just for the Attack Damage. Take this instead of The Bloodthirster

Banshee's Veil
You may think, WTF, Banshee on Renekton. But no, this is very good item against the teams with lots of CC. Take this instead of Force of Nature. Consider taking with Mercury's Threads

About the Skills

Reign of Anger
This is the core of Renekton. Gaining and using Fury. Fury is the key to win. Master using it well. You can gain Fury also when using abilities. For example, autoattack minions to gain almost half of the maximum Fury. Then do the Cull the Meek trick and WHOA, you have full amount of Fury

Cull the Meek (Q)
Mainly for harrassing, farming and gaining health. You should use this ability in the middle of minions to gain max health. And ofc remember to gain Fury first. Very usefull also to harrass two or more enemies at once.

Ruthless Predator (W)
Use this only to enemies and neutral monsters. With Fury and The Black Cleaver this does huge amounts of damage to enemy champion. It also has 1.5 sec Stun and it's great stopping running enemies or preventing them to use their abilities. Use this mainly only with Slice and Dice

Slice and Dice (E)
An unbelievable great ability. Allows you to move fast and take huge shortcuts on the map. It also reduces enemy Armor. A great ability for Harrassing, Chasing and Escaping. You can also Slice and Dice away from Veigar's Event Horizon. This is a great skill to master, you need to know when going back or going to enemy for a kill.

Dominus (R)
With this Renekton becomes a God. You can just run next to enemies and watch them die. They hardly can harm you. You can outrun most of the champs in 1 vs 2 fight with this. You still shouldn't use still all the time. It's way more better to keep this available when needed. Situation where you are about to be ganked or in teamfights. It's useless if you start chasing an enemy and try to put this on. Use this only if enemy is fighting back. REMEMBER TO USE WITH CARE.

Skill Sequence

Because we want to stay in lane for long we start with Cull the Meek. With this we can sweep minions and gain health.

We are still quite vulvenerable and slow we next take the Slice and Dice. Now we are able to harrass the enemy and gain health.

Then we take the Ruthless Predator. At this point the enemy start already to fear you, even with not Dominus. This is the skill we need to get max first.

We take Dominus ofc always we are able to.

After we have maxed the Ruthless Predator we start putting points to Cull the Meek and Slice and Dice depending on which we need most at the time. Slice and Dice Fury bonus is good to have against heavily armored champs, and Cull the Meek when we are taking much damage.

Laning

Renekton is a very good sololaner because of his lifesteal-ability and farming skills. You don't need to go B ever.

5 vs 5:Renekton is at the best in 1 vs 2 sololane. It can also be played in mid.

3 vs 3:
The best place is the top lane, because the ability of fast kill minions and Slice and Dice to upper jungle to get extra XP.

Harrassing and Killing

Fury is the main thing you should gain first. But Harrassing is also possible without the starting amount of fury. (maybe even better, because Slice and Dice uses Fury if you have it already.

Slice and Dice trough the enemy minions (you will get enough fury with this), use Ruthless Predator to enemy, hit Cull the Meek to damage more and gain health and Slice and Dice back to safe distance (E W Q E)

If you think that you are able to slay the enemy use Slice and Dice to catch the fleeing enemy and kill him/her

Again, Remember to use Dominus wisely. Just hitting it and going for a kill is gonna end up for nothing.

Teamfights

As I said, Renekton is a half-tank. What comes to teamfights you can be (not against the all champs) in the center of action and do hell of a lot amounts of damage and tank more than real tanks. Ofc, you need Dominus to this.

Jungling

Jungling, starting at the beginning with Renekton isn't efficient. But after you catch up some level, and the game is in that point that you can move around you should always kill some neutral monsters while running around. (but, don't steal the junglers exp.) For example in TT, Renekton is a very good solo laner (top) Because of Slice and Dice and ability to fastkill neutrals.

Farming

Renekton is a great farmer. At the low levels, you should wait and single hit minions until a minion-group is at low hp, then just Slice and Dice, Cull the Meek and Slice and Dice back ( E Q E ).

At higher levels you can do the same with full healthed minions and neutral monsters.

Other Notable Things

There are two champs that outrun Renekton on 1 vs 1 even they were level 1 and you were level 18. Warwick and Malzahar. If you are against one of these, ask if you can change the lane.